Performance And Mechanisms Of The Graphite Felt Electrode In Electro-chemical System And Electro-fenton System For The Removal Of Microcystis Aeruginosa

Eutrophication,one of the most common causes of water quality deterioration in inland and marine waters,is most visually manifested by toxic cyanobacterial blooms in lakes and waterways,and the proliferation of green algae in coastal areas.Since the 19th century,many rivers,lakes,estuaries and coastal seas on a global scale have generally experienced varying degrees of nutrient status problems.Severe nutrient enrichment has led to serious degradation of aquatic ecosystem functions,especially,the frequent outbreaks of cyanobacterial blooms have posed a great threat to drinking water safety and the natural water environment.Majority of the traditional algae removal methods such as mechanical salvage,coagulation and sedimentation,and the addition of oxidants,however,have certain limitations.Thus,there is an urgent need to develop efficient and eco-friendly technologies assisting with controlling and reducing cyanobacterial reproduction to alleviate these water quality conditions.Electrochemical advanced oxidation technology is very promising for sewage and wastewater treatment because of its high oxidation capacity and environmental compatibility.Electro-Fenton technology,one of the electrochemical advanced oxidation technologies,has attracted much attention due to its excellent oxidation and mineralization capacity.On this basis,the GF-Pt electrochemical system with graphite felt（GF）as the anode and platinum flake（Pt）as the cathode,and the Pt-GF electro-Fenton system by simple switching electrodes were constructed in this paper,respectively,to investigate the performance and mechanism of Microcystis aeruginosa removal and the treatment efficiency of simulated algal bloom water samples,which aimed to provide a reference for the development and application of electrochemical oxidation technology to tackle the problems related to cyanobacterial bloom.The main research contents and conclusions are as follows.（1）Mechanism and performance of graphite felt as anodes in electrochemical system for Microcystis aeruginosa removal.The ideal conditions for the GF-Pt system for M.aeruginosa removal were explored via three parameters:current intensity,anodic area,and initial pH.The biological mechanism of the GF-Pt system for M.aeruginosa removal by electrochemical processes was investigated via monitoring the release and degradation of algal organic matter.Combined with the GF anode material characterization analysis,mechanism study tests and active oxide assay to elucidate the mechanism of algal removal.Without the addition of chemicals,our GF-Pt system operated at pH of 7 and current intensity of 75 mA,achieving removal efficiency of algal cells and MC-LR of 94%and 50%,respectively,in 30 min.The GF-Pt system has a wide pH range and achieves more than 90%algal removal efficiency at pH 3～9.The removal mechanisms operated through direct discharging on the anodes,based on electro-adsorption,and through functional group synergy on the anode surface.（2）Mechanism and performance of the Pt-GF electro-Fenton system for Microcystis aeruginosa removalThe optimal working conditions of the Pt-GF system were sought by single-factor test and response surface methodology,and the changes in physiological characteristics of algae in the electrolytic process were analyzed.The effect of pH conditions on the Pt-GF system for the removal of algal cells and algal organic matter was investigated.The algal removal mechanisms were analyzed by reactive oxygen species detection,iron ion concentration determination and free-radical quenching experiments.The optimal operating conditions of the Pt-GF system were pH of 3,current intensity of75 mA and Fe²⁺concentration of 0.2 mM.In this circumstance,the removal efficiency of algal cells and microcystin-LR were 96%and 83%,respectively,and the algal removal mechanism in the Pt-GF system was figured as homogeneous and non-homogeneous electro-Fenton accompanied by a small amount of electro-flocculation.Notably,the cooperative algae cell removal mechanism in unfavorable pH condition（pH 7）of the Pt-GF system consisted of homogeneous and non-homogeneous electro-Fenton action and electro-flocculation.（3）Study of the GF-Pt system and the Pt-GF electro-Fenton system for simulated algae bloom water samples treatmentExperiments were constructed to investigate the effects of common components（total nitrogen,total phosphorus）of eutrophic waters on the removal of M.aeruginosa by the GF-Pt system and the Pt-GF electro-Fenton systems,and to investigate the treatment efficiency of these two systems on simulated algal bloom water samples.It was shown that the algal removal efficiency of the GF-Pt system was 90%and above in all of single-factor tests.This system could also effectively remove phytoplankton from the simulated algal bloom water samples,especially for cyanobacteria and green algae.In the single-factor test of the Pt-GF system,with the increase of nitrogen and phosphorus content,the algal removal efficiency varified from 96 to 89%,and from 97 to 91%,respectively.Further more,the Pt-GF system could effectively remove phytoplankton and organic pollutants from the simulated algal bloom water samples.In conclusion,the GF-Pt electrochemical system and the Pt-GF electro-Fenton system proposed in this paper can effectively remove M.aeruginosa and algal organic matter,which provided feasible reference for the further study of the application of electrochemical oxidation technology in cyanobacterial water bloom treatment.